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| League History Index | Players | Teams | Managers | Leagues | Leaderboards | Awards | Accomplishments |
| Player | From-To | Avg | HR | RBI | W | L | SV | ERA | K |
|---|---|---|---|---|---|---|---|---|---|
| Brennan O'Bannon | 2021-2022 | .000 | 0 | 0 | 6 | 7 | 0 | 4.16 | 64 |
| Jake O'Brien | 2016-2017 | .000 | 0 | 0 | 9 | 3 | 0 | 2.58 | 118 |
| Matt O'Brien | 2024-2025 | .290 | 9 | 61 | 0 | 0 | 0 | 0.00 | 0 |
| Jim O'Connell | 2019-2020 | .083 | 0 | 1 | 0 | 0 | 0 | 0.00 | 0 |
| John O'Connell | 2025-2025 | .000 | 0 | 0 | 2 | 5 | 0 | 4.74 | 38 |
| Darin O'Connor | 2025-2026 | .247 | 1 | 24 | 0 | 0 | 0 | 0.00 | 0 |
| Mick O'Connor | 2025-2025 | .241 | 0 | 4 | 0 | 0 | 0 | 0.00 | 2 |
| Josh O'Donnell | 2021-2021 | .000 | 0 | 0 | 3 | 0 | 0 | 1.57 | 45 |
| Dan O'Grady | 2019-2019 | .000 | 0 | 0 | 1 | 3 | 6 | 1.87 | 36 |
| Ryan O'Hearn | 2019-2024 | .254 | 3 | 33 | 0 | 0 | 0 | 0.00 | 0 |
| Greg O'Keefe | 2025-2025 | .000 | 0 | 0 | 5 | 2 | 0 | 3.55 | 52 |
| Jason O'Keeffe | 2021-2021 | .176 | 0 | 0 | 0 | 0 | 0 | 0.00 | 0 |
| Taylor O'Meara | 2024-2024 | .000 | 0 | 0 | 4 | 1 | 0 | 4.18 | 24 |
| Chase O'Neal | 2021-2023 | .286 | 23 | 109 | 0 | 0 | 0 | 0.00 | 0 |
| Chris O'Neal | 2025-2025 | .000 | 0 | 0 | 5 | 3 | 0 | 4.32 | 61 |
| Chris O'Neal | 2019-2020 | .172 | 2 | 9 | 0 | 0 | 0 | 0.00 | 0 |
| Jody O'Neil | 2018-2018 | .239 | 4 | 22 | 0 | 0 | 0 | 0.00 | 0 |
| Ross O'Rourke | 2018-2020 | .000 | 0 | 0 | 2 | 2 | 0 | 5.73 | 51 |
| John O'Tey | 2018-2019 | .285 | 30 | 86 | 0 | 0 | 0 | 0.00 | 0 |
| Tim Ocampo | 2022-2023 | .255 | 11 | 61 | 0 | 0 | 0 | 0.00 | 0 |
| Alex Oceguera | 2022-2025 | .000 | 0 | 0 | 2 | 2 | 0 | 3.47 | 45 |
| Billy Ochoa | 2021-2021 | .000 | 0 | 0 | 5 | 5 | 2 | 2.79 | 57 |
| Tae-geun Ock | 2020-2021 | .268 | 4 | 28 | 0 | 0 | 0 | 0.00 | 0 |
| Jeff Odenweller | 2025-2025 | .000 | 0 | 0 | 0 | 0 | 0 | 0.00 | 0 |
| Chris Odette | 2018-2023 | .235 | 15 | 47 | 0 | 0 | 0 | 0.00 | 0 |
| David Ogden | 2025-2026 | .000 | 0 | 0 | 1 | 2 | 4 | 2.72 | 37 |
| Fadeyka Oistrah | 2026-2026 | .000 | 0 | 0 | 0 | 0 | 0 | 0.00 | 1 |
| Joel Ojeda | 2020-2024 | .297 | 11 | 77 | 0 | 0 | 0 | 0.00 | 0 |
| Makoto Okamura | 2025-2025 | .248 | 3 | 23 | 0 | 0 | 0 | 0.00 | 0 |
| Wei-Tzu Oki | 2023-2026 | .000 | 0 | 0 | 5 | 6 | 9 | 5.00 | 101 |
| Player | From-To | Avg | HR | RBI | W | L | SV | ERA | K |
| Shoshi Okuyama | 2026-2026 | .000 | 0 | 0 | 0 | 2 | 0 | 5.40 | 7 |
| Jesus Olavarria | 2026-2026 | .000 | 0 | 0 | 0 | 1 | 0 | 4.72 | 17 |
| Miguel Olea | 2022-2022 | .000 | 0 | 0 | 0 | 1 | 0 | 6.23 | 3 |
| Roberto Olivas | 2021-2026 | .292 | 14 | 91 | 0 | 0 | 0 | 0.00 | 0 |
| Willie Olivas | 2021-2026 | .000 | 0 | 0 | 4 | 7 | 1 | 7.46 | 36 |
| Noah Oliver | 2022-2023 | .000 | 0 | 0 | 4 | 4 | 0 | 2.91 | 106 |
| Alix Ollivier | 2020-2021 | .199 | 3 | 24 | 0 | 0 | 0 | 0.00 | 0 |
| Clayton Ollivier | 2023-2023 | .500 | 1 | 3 | 1 | 2 | 0 | 4.02 | 13 |
| Gary Olsen | 2024-2024 | .000 | 0 | 0 | 4 | 0 | 0 | 7.06 | 21 |
| Cory Olson | 2016-2019 | .000 | 0 | 0 | 7 | 11 | 1 | 3.51 | 167 |
| Justin Olson | 2021-2021 | .194 | 4 | 13 | 0 | 0 | 0 | 0.00 | 0 |
| Mike Olson | 2020-2020 | .000 | 0 | 0 | 4 | 8 | 0 | 3.72 | 69 |
| Preston Olson | 2026-2026 | .000 | 0 | 0 | 2 | 1 | 2 | 1.28 | 22 |
| Robbie Olson | 2024-2026 | .260 | 3 | 14 | 0 | 0 | 0 | 0.00 | 0 |
| John Olund | 2021-2021 | .295 | 3 | 37 | 0 | 0 | 0 | 0.00 | 0 |
| Katsushi Onishi | 2025-2025 | .000 | 0 | 0 | 0 | 1 | 1 | 9.82 | 1 |
| Kazuhiro Ono | 2025-2026 | .000 | 0 | 0 | 3 | 3 | 8 | 2.78 | 68 |
| Khaled Onyebuchi | 2023-2025 | .000 | 0 | 0 | 6 | 2 | 1 | 2.42 | 55 |
| David Openshaw | 2021-2026 | .259 | 1 | 16 | 0 | 0 | 0 | 0.00 | 0 |
| Vinny Oquendo | 2023-2025 | .232 | 6 | 56 | 0 | 0 | 0 | 0.00 | 0 |
| Juan Ordonez | 2022-2022 | .241 | 0 | 8 | 0 | 0 | 0 | 0.00 | 0 |
| Roberto Ordonez | 2022-2024 | .194 | 3 | 14 | 0 | 0 | 0 | 0.00 | 0 |
| Danny Orduna | 2016-2025 | .236 | 3 | 17 | 0 | 0 | 0 | 0.00 | 0 |
| Mario Orduna | 2024-2024 | .000 | 0 | 0 | 4 | 0 | 2 | 5.26 | 38 |
| Blaine Orea | 2022-2024 | .235 | 4 | 21 | 0 | 0 | 0 | 0.00 | 0 |
| Jeremy Orejuela | 2023-2023 | .000 | 0 | 0 | 4 | 3 | 0 | 5.98 | 53 |
| Heath Orlowski | 2025-2026 | .000 | 0 | 0 | 3 | 4 | 4 | 3.17 | 68 |
| Shane Orman | 2018-2025 | .213 | 15 | 59 | 0 | 0 | 0 | 0.00 | 0 |
| Vince Orman | 2019-2026 | .229 | 27 | 115 | 0 | 0 | 0 | 0.00 | 0 |
| Luis Oropeza | 2023-2023 | .000 | 0 | 0 | 1 | 0 | 0 | 4.42 | 6 |
| Player | From-To | Avg | HR | RBI | W | L | SV | ERA | K |
| Jose Orozco | 2026-2026 | .000 | 0 | 0 | 1 | 0 | 0 | 4.26 | 6 |
| Philip Orpen | 2026-2026 | .211 | 0 | 1 | 0 | 0 | 0 | 0.00 | 0 |
| Luis Orta | 2023-2025 | .000 | 0 | 0 | 6 | 5 | 15 | 2.48 | 121 |
| Antonio Ortega | 2022-2022 | .000 | 0 | 0 | 5 | 4 | 0 | 3.16 | 49 |
| Bill Ortega | 2026-2026 | .239 | 4 | 12 | 0 | 0 | 0 | 0.00 | 0 |
| Alex Ortiz | 2020-2023 | .250 | 4 | 39 | 0 | 0 | 0 | 0.00 | 0 |
| Bobby Ortiz | 2020-2026 | .228 | 12 | 54 | 0 | 0 | 0 | 0.00 | 0 |
| Carlos Ortiz | 2022-2026 | .261 | 10 | 45 | 0 | 0 | 0 | 0.00 | 0 |
| Melvin Ortiz | 2018-2026 | .167 | 0 | 4 | 0 | 0 | 0 | 0.00 | 0 |
| Vince Ortiz | 2019-2020 | .000 | 0 | 0 | 5 | 3 | 0 | 1.66 | 48 |
| Flynn Orton | 2023-2025 | .273 | 5 | 34 | 0 | 0 | 0 | 0.00 | 0 |
| Barney Osborne | 2025-2026 | .000 | 0 | 0 | 4 | 2 | 7 | 4.84 | 31 |
| Jacob Osborne | 2026-2026 | .293 | 1 | 5 | 0 | 0 | 0 | 0.00 | 0 |
| John Osborne | 2025-2025 | .000 | 0 | 0 | 0 | 0 | 1 | 3.86 | 13 |
| Jim Ostby | 2022-2026 | .239 | 5 | 21 | 0 | 0 | 0 | 0.00 | 0 |
| Allen Ostrom | 2025-2026 | .221 | 2 | 19 | 0 | 0 | 0 | 0.00 | 0 |
| Kunio Ota | 2022-2026 | .284 | 4 | 28 | 0 | 0 | 0 | 0.00 | 0 |
| Sachiko Ota | 2024-2026 | .272 | 1 | 23 | 0 | 0 | 0 | 0.00 | 0 |
| Tsuneyoshi Ota | 2023-2023 | .000 | 0 | 0 | 1 | 2 | 0 | 4.50 | 34 |
| Emanuel Otero | 2023-2023 | .000 | 0 | 0 | 0 | 1 | 1 | 1.35 | 13 |
| Paul Otero | 2020-2021 | .255 | 9 | 48 | 0 | 0 | 0 | 0.00 | 0 |
| Kevin Ottman | 2024-2025 | .302 | 27 | 104 | 0 | 0 | 0 | 0.00 | 0 |
| Nelle Oudijk | 2021-2024 | .000 | 0 | 0 | 5 | 4 | 1 | 6.50 | 44 |
| Mike Ousley | 2018-2020 | .205 | 8 | 34 | 0 | 0 | 0 | 0.00 | 0 |
| Austin Overend | 2025-2026 | .157 | 2 | 8 | 0 | 0 | 0 | 0.00 | 0 |
| Ryan Overholt | 2024-2026 | .243 | 1 | 6 | 0 | 0 | 0 | 0.00 | 0 |
| Bob Owens | 2023-2024 | .000 | 0 | 0 | 3 | 4 | 0 | 2.65 | 86 |
| Justin Owens | 2026-2026 | .000 | 0 | 0 | 0 | 0 | 0 | 1.35 | 7 |
